Endurance exercise training elicits physiological adaptations which increase the functional capacity of various organs. Older, physically well-trained "master" athletes tend to have a cardiovascular functional capacity (VO2 max) which more closely approximates that of much younger individuals than that of their sedentary peers. They also have higher levels of high density lipoprotein (HDL) cholesterol, lower percent body fat and are more insulin sensitive than age-matched sedentary controls. To examine the interrelationship of age and physical fitness to endocrinemetabolic function, a study was designed to compare lipid profiles and metabolism, glucose metabolic rates and insulin sensitivity, and cardiovascular function in highly trained older men (greater than 50 years of age) with their sedentary peers as well as with highly trained young individuals. The role of training in the highly trained individuals will be examined by de-training them over a 10 day period. Endocrine-metabolic function studies include 1) glucose tolerance, beta cell sensitivity, and insulin sensitivity using oral glucose challenge (OGTT) and hyperglycemic clamp techniques, 2) lipoprotein metabolism and lipoprotein lipase activity, 3) sympathoadrenal response to isometric exercise (handgrip), upright posture and hyperglycemic clamp. Of 102 regularly exercising men, 50 to 86 years of age, enrolled in the program since June 1985, baseline fasting glucose and lipid profiles have been obtained on 42 of the most highly active participants. Thirteen of these have also undergone an initial treadmill screening test and maximal oxygen consumption (VO2max) test, 5 have undergone a second VO2max test and thallium scan, and 4 have undergone oral glucose tolerance (OGTT) and isometric exercise (handgrip) tests. Preliminary lipid profiles confirm high levels of HDL cholesterol in these very active older men.